The present invention relates generally to process control systems and, more particularly, to a process control configuration system having a configuration database that can be accessed and updated from geographically distributed physical locations within a process control system.
Process control systems, like those used in chemical, petroleum or other processes, typically include at least one process controller communicatively coupled to at least one host device or operator workstation and to one or more field devices via analog and/or digital buses or other communication lines or channels. The field devices, which may be, for example, valves, valve positioners, switches, transmitters (e.g., temperature, pressure and flow rate sensors), etc. perform functions within the process such as opening or closing valves and measuring process parameters. During runtime of a process, the process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices via an input/output (I/O) device, uses this information to implement a control routine and then generates control signals which are sent over the buses or other communication channels via the input/output device to the field devices to control the operation of the process. Information from the field devices and the controller is typically made available during runtime to one or more applications executed by the operator workstation to enable an operator to perform any desired function with respect to the process, such as viewing the current state of the process. Additionally, configuration applications executed on a user interface, such as a host device, workstation, laptop computer, etc. may be used to modify the operation of the process, configure the process, view the configuration of the process, document the process configuration, etc.
Generally speaking, process control systems are configured using a configuration database that stores configuration information pertaining to each of the hardware and software elements within the process control system, the manner in which the hardware elements, such as different devices and controllers in the process, are physically interconnected and the manner in which different software elements, such as control modules, communication modules, etc., are associated with and executed by the different devices within the process control system to perform process control. In some cases, the configuration database is an object-oriented database that stores configuration objects or components for each different logical element of a process control system as objects. The configuration database may, for example, include a library that stores object templates for some or all of the hardware and software elements, these templates being used to create configuration objects for instances of hardware or software elements actually used within the process control system. The configuration database may also include setup or physical network sections that define the manner in which the physical elements of a process control system are set up, distributed and connected together. In some cases, the configuration database also includes a control section that defines how control is performed using controllers, field devices and control modules or control routines executed in the controllers and/or the field devices. During configuration of the process control system, a configuration routine or application executed in, for example, a user interface or workstation, is used to create or modify the configuration database to reflect the actual configuration of the process control system. This configuration application typically uses the information within the configuration database to configure devices, controllers, etc. associated with the process control system and stores new configuration information in the configuration database after any configuration activity is performed, such as when a device or software element is added to the system, changed, etc.
Still further, the configuration database is generally used to display the current configuration of the process control system to users via user interfaces connected to the process control system. In the past, some of the process control system user interfaces, configuration databases and controllers were communicatively connected together by a dedicated bus, such as an Ethernet bus, to form a local area network (LAN). Because the dedicated Ethernet bus has a large bandwidth, and because any particular signal or data request sent over the Ethernet bus does not have to travel over a very long distance within the LAN, communication with the configuration database by one of the user interfaces is fairly straightforward and fast in these systems. As a result, configuration display routines executed in the user interfaces typically access and retrieve configuration information from the configuration database each time the user indicates or requests information pertaining to the configuration of the process control system. This retrieved information is then sent out over the Ethernet bus and is displayed to the user at the user interface. Because of speed (or high bandwidth) of the dedicated Ethernet bus, multiple users can access the configuration database relatively simultaneously and can view the same or different configuration data pertaining to the configuration of the process control system. Similarly, different users can reconfigure different parts of the process control system because any new configuration data that was generated was able to be provided directly to the configuration database in a relatively short amount of time via the dedicated Ethernet bus. Still further, because only those devices connected to the LAN can access the configuration database, and because the LAN is typically limited to a single process location, there is not much need to enable a large number of user interfaces to access the configuration database simultaneously.
Recently, however, there has been a general increase in the size of some process control systems and there has been a desire to integrate configuration information for process control networks spread out or distributed over larger or separated geographical areas. For example, some users wish combine the configuration data associated with different process sites, which may be in different counties, states or even different countries, thereby allowing an operator at a first site to access and view configuration information about a second site and possibly even perform configuration activities that effect the second site from the first site. In another example, a user may wish to integrate an oil well located on a platform many miles out in the ocean with an oil refinery process control system having numerous controllers, user interfaces, etc. located on the mainland. In this case, it is desirable to enable a user at the oil refinery site to reconfigure or effect the configuration of the devices on the oil well platform without actually having to fly out to the platform, connect a user interface to a terminal on the oil well platform and reconfigure the oil well controller, as is typically necessary now. Still further, with the integration of multiple process control sites, the number of user interfaces which may be used to simultaneously access the configuration databases of these sites increases significantly.
When integrating multiple geographically separated sites, however, it is practically, if not actually, impossible to connect the different sites using a common dedicated bus, such as the Ethernet bus, due to the distances involved. It is possible, however, to use a satellite, cellular or other type of wireless link or a wide, area network link, such as the Internet, or T1 lines, to establish a communication connection between the different sites of a process control system, to thereby enable the integration of geographically separated portions of a process control network. However, satellite, cellular and other wide area wireless communication links are typically very expensive to use and, if used, are generally shared so that they can only provide a limited amount of bandwidth when compared to a dedicated bus, such as an Ethernet bus. Likewise, the Internet, T1 lines and other shared wide area networks provide only a limited amount of bandwidth or throughput and are, therefore, typically very slow for data transfer when compared to a dedicated Ethernet local area network bus. Still further, the geographical distance between the different sites and the need to provide secure and assured communications between the sites using, for example, acknowledgments of data packets, as provided in the IP, TCP and UDP communication protocols, further add to the delay of communications between the sites.
As a result of the delay in communications between geographically diverse sites of a process control system and the increase in the number of user interfaces or other devices accessing a configuration database, it is difficult to provide a configuration database that stores the data for the entire process control system, including the devices in each of the geographically diverse sites in a manner that can be accessed in a fashion by users at all of the different sites and in a manner that can altered by users at the different sites using current configuration database accessing procedures. Specifically, if the configuration database is located at a main site, users at a remote site will have to download all of the configuration data on a refresh basis over the slow or remote link, which may take an inordinate amount of time. Still further, the sheer increase in the number of users accessing the configuration database may increase the access time to any piece of information within the configuration database to an unacceptable level. Likewise, when reconfiguring the process control system, the delay in communications between a main site and a remote site may enable two different users to try to reconfigure the same component of the process control system leading to confusion and error. Thus, for example, a user at a remote site may request and obtain the current configuration of the process from the configuration database at the main site, may reconfigure a portion of the process control system at the remote site and then send the new configuration data to the configuration database at the main site. In the meantime, however, a user at the main:site may reconfigure the same portion of the process control system and, because there is relatively no delay in communications at the main site, may store this new configuration in the configuration database before the user at the remote site attempts to send new configuration data generated at the remote site to the configuration database for storage, which leads to errors.
In some cases, it may not be possible or practical to even provide a slow or low bandwidth communication link between different sites, in which case configuration of a remote site has to occur at the remote site and then has to be uploaded to the configuration database at the main site. However, this off-line configuration can cause problems if different users try to reconfigure the remote site at or near the same time, or if a user tries to reconfigure a remote site before another user who has already reconfigured the remote site updates the configuration database to reflect the changes already made to the remote site.
A configuration database distribution, access and alteration strategy is provided to enable numerous geographically separated locations of a process control system to be integrated together using a common configuration database in a manner that enables users at each of the different locations to view and change the configuration database in a timely, secure and non-conflicting manner, even when the different locations of the process control system are communicatively connected via a low bandwidth or slow (i.e., delayed) communication link or are only intermittently communicatively connected via, for example, a modem connection.
According to one aspect of the invention, a distributed configuration database is provided having components thereof spread over or throughout the different geographical portions of a process control system in such a manner that shared configuration data, i.e., configuration data pertaining to or applicable to more than one location, is stored in a database assessable by each of the other locations via one or more slow or low bandwidth communication links and data that pertains only to a particular location is stored in a configuration database at that location. In this manner, the configuration information that is most likely to be accessed at a particular location (i.e., the configuration information pertaining to that location) is accessible over a local area network while configuration information pertaining to other locations is accessible over a slow or low bandwidth communication link. As a result, only shared communication data and data that is related to a different location needs to be sent over a slow or low bandwidth communication link.
To prevent configuration data being viewed by users within the process control system from becoming stale, the configuration database access system at each location may automatically send changes made to the configuration database to each of the users currently viewing that data so that the user views the state of the configuration as it actually exists in the configuration database. In one embodiment, each portion of the configuration database includes a data access routine that uses a shared cache to coordinate the delivery of configuration components to each of the users or subscribers currently viewing that data in a way that reduces the number of reads to the configuration database, which increases the speed of accessing data from the configuration database. This shared cache may incorporate a locking mechanism to enable locking and reservation of components within the configuration database. If desired, the configuration information obtained by each user may be stored locally to enable the user to view the configuration information even if the communication link to the configuration database storing the master copy of that information goes down or otherwise becomes unavailable.